'\" et
.TH ALIAS "1P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
alias
\(em define or display aliases
.SH SYNOPSIS
.LP
.nf
alias \fB[\fIalias-name\fB[\fR=\fIstring\fB]\fR...\fB]\fR
.fi
.SH DESCRIPTION
The
.IR alias
utility shall create or redefine alias definitions or write the values
of existing alias definitions to standard output. An alias definition
provides a string value that shall replace a command name when it is
encountered; see
.IR "Section 2.3.1" ", " "Alias Substitution".
.P
An alias definition shall affect the current shell execution
environment and the execution environments of the subshells of the
current shell. When used as specified by this volume of POSIX.1\(hy2017, the alias definition
shall not affect the parent process of the current shell nor any
utility environment invoked by the shell; see
.IR "Section 2.12" ", " "Shell Execution Environment".
.SH OPTIONS
None.
.SH OPERANDS
The following operands shall be supported:
.IP "\fIalias-name\fR" 10
Write the alias definition to standard output.
.IP "\fIalias-name\fP=\fIstring\fR" 10
.br
Assign the value of
.IR string
to the alias
.IR alias-name .
.P
If no operands are given, all alias definitions shall be written to
standard output.
.SH STDIN
Not used.
.SH "INPUT FILES"
None.
.SH "ENVIRONMENT VARIABLES"
The following environment variables shall affect the execution of
.IR alias :
.IP "\fILANG\fP" 10
Provide a default value for the internationalization variables that are
unset or null. (See the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 8.2" ", " "Internationalization Variables"
for the precedence of internationalization variables used to determine
the values of locale categories.)
.IP "\fILC_ALL\fP" 10
If set to a non-empty string value, override the values of all the
other internationalization variables.
.IP "\fILC_CTYPE\fP" 10
Determine the locale for the interpretation of sequences of bytes of
text data as characters (for example, single-byte as opposed to
multi-byte characters in arguments).
.IP "\fILC_MESSAGES\fP" 10
.br
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard error.
.IP "\fINLSPATH\fP" 10
Determine the location of message catalogs for the processing of
.IR LC_MESSAGES .
.SH "ASYNCHRONOUS EVENTS"
Default.
.SH STDOUT
The format for displaying aliases (when no operands or only
.IR name
operands are specified) shall be:
.sp
.RS 4
.nf

"%s=%s\en", \fIname\fR, \fIvalue\fR
.fi
.P
.RE
.P
The
.IR value
string shall be written with appropriate quoting so that it is suitable
for reinput to the shell. See the description of shell quoting in
.IR "Section 2.2" ", " "Quoting".
.SH STDERR
The standard error shall be used only for diagnostic messages.
.SH "OUTPUT FILES"
None.
.SH "EXTENDED DESCRIPTION"
None.
.SH "EXIT STATUS"
The following exit values shall be returned:
.IP "\00" 6
Successful completion.
.IP >0 6
One of the
.IR name
operands specified did not have an alias definition, or an error
occurred.
.SH "CONSEQUENCES OF ERRORS"
Default.
.LP
.IR "The following sections are informative."
.SH "APPLICATION USAGE"
None.
.SH EXAMPLES
.IP " 1." 4
Create a short alias for a commonly used
.IR ls
command:
.RS 4 
.sp
.RS 4
.nf

alias lf="ls -CF"
.fi
.P
.RE
.RE
.IP " 2." 4
Create a simple ``redo'' command to repeat previous entries in the
command history file:
.RS 4 
.sp
.RS 4
.nf

alias r=\(aqfc -s\(aq
.fi
.P
.RE
.RE
.IP " 3." 4
Use 1K units for
.IR du :
.RS 4 
.sp
.RS 4
.nf

alias du=du\e -k
.fi
.P
.RE
.RE
.IP " 4." 4
Set up
.IR nohup
so that it can deal with an argument that is itself an alias name:
.RS 4 
.sp
.RS 4
.nf

alias nohup="nohup "
.fi
.P
.RE
.RE
.SH RATIONALE
The
.IR alias
description is based on historical KornShell implementations. Known
differences exist between that and the C shell. The KornShell version
was adopted to be consistent with all the other KornShell features in
\&this volume of POSIX.1\(hy2017, such as command line editing.
.P
Since
.IR alias
affects the current shell execution environment, it is generally
provided as a shell regular built-in.
.P
Historical versions of the KornShell have allowed aliases to be
exported to scripts that are invoked by the same shell. This is
triggered by the
.IR alias
.BR \-x
flag; it is allowed by this volume of POSIX.1\(hy2017 only when an explicit extension such as
.BR \-x
is used. The standard developers considered that aliases were of use
primarily to interactive users and that they should normally not affect
shell scripts called by those users; functions are available to such
scripts.
.P
Historical versions of the KornShell had not written aliases in a
quoted manner suitable for reentry to the shell, but this volume of POSIX.1\(hy2017 has made
this a requirement for all similar output. Therefore, consistency was
chosen over this detail of historical practice.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "Section 2.9.5" ", " "Function Definition Command"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "Chapter 8" ", " "Environment Variables"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
